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Old 11-07-2014, 06:45 PM   #1
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Big tanks aging fuel

Today I toped off my fuel tanks for the winter season. Since I use the boat about 2 hours every two weeks over the winter I may not have to do it again for a while. On the same dock friends of mine with a Kady Krogen took over one thousand gallons. They went to Alaska this summer. I notice that a lot of the trawlers with big tanks don't go long distance every year. I know that some have circulating filtration but still that's a lot of fuel to sit around ageing. Over a couple of years if only a fraction of the fuel is renewed each season the engines have to be running on suboptimal fuel. This of course does not apply to the boats constantly on the move. What are some of the strategies used if any to handle this other than polishing which may not stop all the ageing effects?
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Old 11-07-2014, 07:35 PM   #2
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That fuel is no good at all when it gets old!! You need to give it to me and I will charge just a little fee to take it off your hands. What I will really do is load it in my boat and go to the Caribbean!!!

In all seriousness, diesel can last for years. I recommend a biocide. Also I think there are stabilizers that reduce aging, but I don't know much about them. Others may know more...

I have unloaded diesel that was like 7-10yrs old off a boat due to owner's request. Tank had some serious gunk in bottom, but the fuel went into my boat and TDI Jetta. No problems with either.

I think many hospital and power plant backup gennies have very old fuel- I don't know what their strategies are but they take that stuff seriously and that should be the strategy you use.
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Old 11-07-2014, 08:14 PM   #3
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Just did a quick net search on old diesel fuel. Many old tractors with old fuel seem to run. One statement from stand by generator service person said many problems from old and poor fuel. What about newer common rail motors are they not very sensitive to clean good fuel quality. One statement sounding official said after one or two years the fuel when tested is usually out of spec. I suppose diesels can be tough buggers and run on old fuel. There were also multiple descriptions of how to doctor old fuel.
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Old 11-07-2014, 09:02 PM   #4
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Our strategy for dealing with old fuel on the boat is not to have any.

We have five tanks; a day tank that feeds the engines and generator and four saddle tanks that are used to fill the day tank via gravity and manual valves when the day tank gets low.

Unless we are going to take a longer cruise, we leave one oposing pair of saddle tanks empty. When the other pair has been drawn to about a quarter full by using the boat, we fill the empty pair. We continue to draw down the first pair until they are totally empty (all tanks drain/feed from the bottom) and then we let them sit empty until we have drawn down the second pair to about a quarter full.

So the proccess of staggering the full and empty tanks simply repeats itself.

This process has worked great over the 16 years we've had the boat. The longest fuel is on the boat before being used is probably about six months, give or take.

We use two additives in our fuel, a bug killer and a lubricity booster.
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Old 11-07-2014, 10:32 PM   #5
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Marin that sounds really good. Unfortunately I did not think of that when I built Moon River. I use the boat enough to turn our 400 gallons over in reasonable time. For my first two years I am averaging 250 hours/year. 90% of the time I am burning 4-5 gal/hr and 2 to 3X that for about 8% of the time the remaining 2% is marina speed. Had I elected to go with more tankage I would have liked your set up.
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Old 11-07-2014, 10:40 PM   #6
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I refill two (158 gallons) of four fuel tanks at a time. That lasts about nine months. Then I fill the other tanks. And so on, and so on. (Unless planning a trip to Mexico or the PNW where I'd need maximum range.) Burning fuel at two gallons or less per hour makes for lots of boating time.
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Old 11-07-2014, 10:45 PM   #7
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Had I elected to go with more tankage I would have liked your set up.
In the interest of giving credit where credit is due, it's not my setup. The previous owner of our boat removed the boat's original tankage--- three 150 gallon tanks--- and replaced them with the system I described. I suspect the motivation to do this was the usual suspect; the original iron tanks starting to rust out. The boat was built in late 1973.

The new (as of 1997) setup uses stainless steel tanks, which is both good and bad, and is designed to depend solely on gravity with all tanks including the day tank feeding from their lowest points. So when a tank is empty, it's empty.

It's a very simple system with a degree of flexibility. Each engine can be fed from the day tank or either saddle tank on its side of the boat, and the fuel return can be switched between tanks. However, in normal practice both engines are fed from the day tank and both fuel returns are valved to go to the day tank.
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Old 11-07-2014, 10:49 PM   #8
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... Each engine can be fed from the day tank or either saddle tank on its side of the boat, and the fuel return can be switched between tanks. However, in normal practice both engines are fed from the day tank and both fuel returns are valved to go to the day tank.
Seems most prudent: return to the originating tank.
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Old 11-08-2014, 06:55 AM   #9
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>Over a couple of years if only a fraction of the fuel is renewed each season the engines have to be running on suboptimal fuel.<

Bad fuel has water and bugs , not mere age.
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Old 11-08-2014, 08:20 AM   #10
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FF nailed it from what little I know from my studies and interviews. Diesel does not "age" or get "stale or spoil". Moisture collects on the bottom of the tank (condensation will build up over he years) and cooties grow in that water. They live,breed,crap,and die and that combination is what builds up and clogs your system. Biocide helps control this growth, but does not eliminate the problem nor does it get rid of what is already there.
Bottom tank fuel feed..very lowest place in the tank with out the bottom feed is the best. Second best is a day tank filtering from main to day so you can control filter health well before fuel is needed to run your main. Combination of the two is next to heaven.
I think, if ever I have tanks built, I would leave the bottom of tank open side to side, end to end so a probe could be inserted to properly polish the fuel. Not being able to get the probes in to churn the trub to filter it out is often a problem because of baffle design.
From people in the polishing industry I have been told there is no use by date on diesel.
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Old 11-08-2014, 12:55 PM   #11
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The consensus of opinions on ageing diesel seems to be that the fuel it's self does not (significantly)spoil but water and bugs are the problem and probably the risks increase while sitting around. Does that then imply that continuous or timed polishing would be a good strategy where there are big tanks and little use over long periods. And then there are additives including biocides. I personally like the idea of a system that allows flexibility in how much fuel the boat can carry so long as the empty tanks are really empty and clean.
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Old 11-08-2014, 01:56 PM   #12
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Biggest thing is making sure there is no water in the bottom of the tanks.

I did this when I set up my tanks: the pickup for main engine goes to within 1/4" of the bottom of the tanks, in the lowest corner. If water does get in the tank, it immediately goes into the racor.

My tank fills are on the tanks themselves- you can look inside with a flashlight and see the bottom.

So look at your tank layout. If you can positively know that there is no water, then there is no bug problem.

Still there are some precipitates that drop out of diesel, again if pickups are low they tend to not accumulate in tank and get caught by filter. If pickup is high, they do tend to accumulate in tank bottom, only to get in filter when boat gets tossed around.

So many boats have tank layouts that make maintenance difficult or impossible.
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Old 11-08-2014, 06:04 PM   #13
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Additives and supply management.

We've gone through several thousand gallons this year (two boats) and we currently only have about 450/150 remaining on board them. We will likely only keep this amount on board for the next few months even though fuel is getting really cheap.

Without going into the whole process of catalytic cracking, suffice it to say that today's fuel is inherently unstable. Add to this the fact that marine fuel tanks are not designed for proper fuel storage, but more for transport, I've tried not to not store more than I need for 90 days or so. When I look around at all the fuel related problems on docks I'm convinced this practice actually costs less in the long run.

Btw you might also Google asphaltene precipitation in diesel to see why it's not always a good idea to have your engine return fuel to the main storage tank. Food for thought.



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Old 11-08-2014, 09:56 PM   #14
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Well engines will run on old fuel if it is filtered enough. water and growth secondary to water are the biggest problem. But I do have to inform all that diesel fuel does change with age. There are components of the fuel that interact with oxygen that cause sticky particles to precipitate out. This process starts in 60-90 days and BP suggests safe storage if not hot of 12 months. Certain metal contaminants and heat will increase this process. I think the precipitate is called aspertine or something like that. This stuff makes for sticky black deposits in filters and on tank walls. Good filtration keeps this out of injectors. New common rail motors are particularly sensitive to this and other crud in fuel. The fact that lots of people use old fuel and many say there is no problem does not mean the ageing is totally insignificant. It probably means your filtration is doing its job and or the engine can run on sub optimal fuel. What we don't know based on this practical reporting is weather there is any cumulative long term damage. More than likely there is data somewhere in the Engine and fuel industry that addresses this. Look up BP diesel fuel storage pdf
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Old 11-08-2014, 10:20 PM   #15
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I've been advised to take on fuel and add an additive prior to winterizing. I understand the additive, but what is the benefit of taking on fuel at the beginning of the winter?
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Old 11-08-2014, 11:10 PM   #16
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I've been advised to take on fuel and add an additive prior to wintering.... what is the benefit of taking on fuel at the beginning of the winter?
Reduced condensation?
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Old 11-08-2014, 11:12 PM   #17
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The more air you have in the tank the more condensation you can have. Warm air carries moisture. As the temperature drops the water vapor condenses into water eventually ending up in the bottom of the tank. Bigger air spaces means more air. More air holds more water. So If you fill up before winter you will have less water in the tank in the long run. Of course, a better plan, in my view,(although not one I am following yet ) is to winterize the boat by moving the boat towards the equator at this time of year which should help the whole air too cold thing from causing condensation in your fuel tanks.
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Old 11-08-2014, 11:26 PM   #18
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The more air you have in the tank the more condensation you can have. Warm air carries moisture. As the temperature drops the water vapor condenses into water eventually ending up in the bottom of the tank. Bigger air spaces means more air. More air holds more water. So If you fill up before winter you will have less water in the tank in the long run. Of course, a better plan, in my view,(although not one I am following yet ) is to winterize the boat by moving the boat towards the equator at this time of year which should help the whole air too cold thing from causing condensation in your fuel tanks.

Makes sense. That is our plan too, but we have to get through one more winter first.
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Old 11-09-2014, 01:02 AM   #19
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Yes moving south will help the old fuel problem particularly if you run the boat there on it's own bottom. The extra heat however will increase the rate of aspertine formation so you will still want to keep running your engine when you get there. No hanging out on the hook with a cold margarita in hand.
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Old 11-09-2014, 01:04 AM   #20
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We do not top off our tanks in the winter. In fact, two of them are usually empty all winter long, and the other three are generally partially full. I check the Racor bowls prior to the first startup of a cruise, weekend or otherwise. And in 16 years I have yet to see any water in the Racors.

Now, we keep heat in the engine room during the winter (the temp stays about 50-55 degrees) which may help. And I'm not saying condensation in a fuel tank doesn't happen; we had water in the fuel tanks every morning in the planes I flew in Hawaii even when the planes had been flown the previous day and new fuel put in the tanks in the evening. But for whatever reason, we have never had a condensation problem in the tanks of our boat here in the PNW.
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